The big picture: Plants evolved from green algae


  • Cyanobacteria & protist made landfall ~1.2 bya
    • plants, fungi and animals ~500 mya
    • first forests 385 mya


  • Plants evolved from green algae
    • Several key ‘shared traits’
    • WHAT DO YOU THINK THEY ARE?


  • Plants support all life on earth
    • Oxygen to breath
    • food to eat
    • new habitats

Green Algae (Oedogonium)



  • Sister group to land plants
    • marine and freshwater
    • single and multi-cellular
    • broad, thick filaments
    • some have AoG
    • evolved around ~750mya


  • Reproductive features:
    • Oogonia = egg containing cell
    • Antheridium = sperm containing cell

Molecular evidence points at charophytes as plant ancestors

Charophytes (freshwater green algae)


  • Freshwater species


  • Transition from water to land starts with Charophytes
    • freshwater habitats may have dried
    • a population eventually lived above water line


  • More shared traits with land plants:
    • circular protein rings in plasma membrane; make cellulose fibers in cell wall
    • swimming sperm with similar structure

Land plants are a monophyletic group

All land plants are embryophytes



  • 10 divisions of land plants
    • does not include algae


  • Zygote develops into multicellular embyro, while enclosed in reproductive structure
    • algae do not retain embryo


  • Land plant & embryophyte terms used interchangeably

Multi-cellular, Dependent embryos (placental transfer)

Shared Traits further define plant evolution

Waxy cuticle and stomata

Multi-cellular Gametangia

Photosynthesis with unique pigments (chlorophyll A & B)

Unique cell walls




  • Cells walls made of cellulose
    • not unique to plants


  • Pectin to fortify cell walls
    • unique to plants


  • Produce cells walls in unique way
    • at end of mitosis

Alternation of generations


  • Land plants alterate between diplod (2N) and haploid (1N) generations
    • diploid = sporophyte
    • haploid = gametophyte


  • sex cells (1N) make zygote (2N)
  • zygote → embryo → sporophyte (all mitosis)
  • sporophyte makes spores (1N) by meosis
  • spores germinate into gametophyte (1N) by mitosis
  • gametophyte makes sex cells (sperm and egg)


  • dominance of different generations key for evolution

First plant group: non-vascular bryophytes (mosses)


  • Mosses, hornworts and liverworts
    • Fossils of bryophyte spores ~470mya


  • Non-vascular; ground hugging carpets
    • bodies to thin to support height growth


  • Have a rhizoid but not a root
    • anchors plant
    • does not uptake water


  • Resistant spores

Bryophytes have gametophyte dominated life cycle

Bryophyte diversity and stomatal evolution


  • Not all mosses (early lineages) have stomata
    • some moss stomata are not functional


  • Stomata only on capsule of sporophyte
    • small strucutre on stalk that makes spores


  • Liverworts do not have stomata!
    • what does this mean?

Bryophyte diversity and stomatal evolution


  • Not all mosses (early lineages) have stomata
    • some moss stomata are not functional


  • Stomata only on capsule of sporophyte
    • small strucutre on stalk that makes spores


  • Liverworts do not have stomata!
    • what does this mean?


  • Hornworts look like liverworts but have stomata
    • once open, stomata never close

Byrophyte stomatal evolution (Renzaglia et al. 2017)